When manufacturing/processing a spectacle lens, it is necessary to evaluate the obtained spectacle lens to see whether or not the both optical surfaces thereof have the required optical performance and surface shape set forth in the applicable specification or design. The spectacle lens evaluation is mainly performed by measuring the optical characteristics at measurement point(s) of the lens. Generally, if the spectacle lens is a single-vision lens, then an optical center is selected as the measurement point; if the spectacle lens is a multi-focal lens, then a distance portion optical center and positions for measuring addition power (i.e., a distance portion vertex power measurement point and a near portion reference point) are selected as the measurement points; and if the spectacle lens is a progressive-addition lens, then a distance portion reference point and positions for measuring addition power (i.e., a distance portion reference point and a near portion design reference point) are selected as the measurement points.
Incidentally, measuring methods for measuring the optical characteristics of various kinds of spectacle lenses (the single-vision spectacle lens, the multi-focal spectacle lens and the progressive-addition lens) and allowance for measured value are specified in ISO, JIS and the like.
However, since the wearer of the spectacle lens also sees things through the region other than the measurement point(s) of the lens, there is a desire to develop an evaluation method in which the lens is evaluated in a wide region, instead of being evaluated at the aforesaid measurement point(s) only. For example, it is important to evaluate the lens in a wide region particularly in the case where one or both surfaces of the lens have complicated surface shape, such as a progressive-addition lens.
As prior arts, it is proposed that the lens is evaluated by actually measuring a three-dimensional shape of the lens surface, and the optical characteristics are calculated based on the three-dimensional shape (see, for example, Patent Documents 1 and 3). Further, it is also proposed to provide a method and device to measure the optical characteristics, such as a dioptric power distribution (referred to as a “power distribution” hereinafter), of the lens in a wide region (see Patent Document 2), and evaluate the optical characteristics of the lens based on a difference distribution between a measured power distribution in a wide region and a power distribution obtained based on design data (see Patent Document 4).
An astigmatism distribution (i.e., a distribution of the absolute value of cylindrical power C), an average power distribution [i.e., a power distribution expressed by S+C/2 (herein, S represents spherical power, and C represents cylindrical power)], and the like are used as the measured power distribution.
Further, since the mold used for molding the spectacle plastic lens is formed of glass whose molding surface is transferred to the plastic lens, the molding surface of the mold has to be formed with the same accuracy as that of the surface of the spectacle lens. Thus, in the case where the mold is formed to be conformed to the shape of the lens, the mold can be evaluated in the same manner as the spectacle lens.    Patent Document 1: Japanese Unexamined Patent Application Publication No. H08-304228    Patent Document 2: Published Japanese Translations of PCT International Publication for Patent Application Publication No. H10-507825    Patent Document 3: Japanese Unexamined Patent Applications Publication No. 2000-186978    Patent Document 4: Domestic Re-publication of PCT International Publication for Patent Applications Publication No. WO2003/098181